TWOPORFLOW: A two-phase flow porous media code, main features and validation with BWR-relevant bundle experiments

TWOPORFLOW is a thermal hydraulics code under development, which simulates two-phase flow in a structured or unstructured porous medium using a flexible 3-Dimensional Cartesian geometry. It has the capability to simulate simple 1-D geometries (like heated pipes), fuel assemblies resolving the sub-channel flow between rods, or a complete nuclear reactor core using a coarse mesh. It solves the time-dependent system of six conservation equations i.e. the mass, momentum and energy conservation equations for liquid and vapor in 3-D geometry. This paper describes the conservation equations and the empirical closure correlations of TWOPORFLOW that are relevant to describe the BWR (Boiling Water Reactor) core thermal hydraulics conditions which may occur under normal or off-normal conditions. Afterwards, the code is validated using selected experiments such as the BWR Full-size Fine-mesh Bundle Test (BFBT) benchmark with emphasis on the prediction of the void fraction and the pressure drop along the core for stationary and transient test conditions. Based on the results of the validation work, TWOPORFLOW is able to predict the BWR-thermal hydraulic behavior with satisfactory accuracy compared to other well-known thermal-hydraulic codes.